Antiperspirant products are frequently produced in stick form, such as wax sticks, soap gel sticks, and pressed powder sticks. A wax stick, in addition to the antiperspirant active ingredient, is composed of waxes and esters and contains a relatively high percentage of a solvent. Wax sticks have certain inherent disadvantages in that the waxes have a tendency to stain clothing, and the wax residue cannot be removed from the clothing by normal washing procedures. As the wax stick contains a high proportion of solvent, the solvent will evaporate if the stick is unsealed and exposed to the atmosphere, thereby resulting in shrinkage and "dog-boning" of the stick, with a resulting unattractive appearance.
As the wax stick has a relatively high proportion of solvent, this reduces the proportion of active ingredient that can be included in the stick, limiting the active ingredient to a maximum percentage of about 40%.
Soap gel anti-perspirant sticks have also been used in the past. The conventional soap gel system includes sodium stearate and a low molecular weight alcohol, such as ethanol, as well as an anti-perspirant active ingredient in a maximum amount of about 20%. In addition, soap gel sticks have normally used calcium carbonate as a filler. Because of the hygroscopic nature of the ingredients, the product has a tendency to absorb water, expand and crack. Furthermore, the calcium carbonate filler tends to neutralize the anti-perspirant, which is normally aluminum chlorohydrate, thereby rendering the anti-perspirant salt ineffective. As a further disadvantage, the alcohol will evaporate if the stick is exposed to the atmosphere, causing shrinking and "dog-boning" of the stick.
Attempts have also been made in the past to provide a dry, pressed powder, anti-perspirant stick. In sticks of this type, the active ingredient is incorporated with an inert filler and binder and the dry mixture is compressed or extruded at high pressure into stick form. The compression operation is slow and requires a dwell of several minutes at high pressure, making the process unsatisfactory from a commercial standpoint. Extrusion of the dry mixture is particularly difficult due to the abrasive nature of the dry powdered mixture. Further, in both compressing and extruding processes, the anti-perspirant active ingredient is damaging to the expensive processing equipment.